1. Field of the Invention
The invention relates to a two-step dicing operation for forming a front face of an ink jet print element. The first dicing cut dices from the bottom side of the print element and provides a back cut relief feature on the front bottom side of the print element. The second dice cut dices from the top side of the print element to form a finished front nozzle face and completely sever the front of the print element from a wafer.
2. Description of Related Art
Thermal ink jet printing, though capable of continuous stream operation, is generally a type of drop- on-demand ink jet system. In such a system, an ink jet printhead expels ink droplets on demand by selective application of a current pulse to a thermal energy generator, usually a resistor, located in capillary-filled, parallel ink channels a predetermined distance upstream from channel nozzles. The channel end opposite the nozzles are in communication with a small ink reservoir to which a larger external ink supply is connected.
Ink jet printheads are composed of two parts, a channel plate and a heater plate, aligned and bonded together. The heater plate is a substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes. The channel plate is a substrate having at least one recess anisotropically etched therein to serve as an ink supply manifold when the two parts are bonded together. A linear array of parallel grooves are also formed in the channel part. One end of the grooves communicates with the manifold recess and the other end is open for use as an ink droplet expelling nozzle. Many printheads are formed by producing a plurality of sets of heating element arrays with their addressing electrodes on a silicon wafer and by placing alignment marks thereon at predetermined locations. A corresponding plurality of sets of channel grooves and associated manifolds are produced in a second silicon wafer. Alignment openings are etched in the second silicon wafer at predetermined locations. The two wafers are aligned via the alignment openings and alignment marks, then bonded together and diced into many separate printheads.
Most known ink jet print elements include a forward step projection on a lower front portion of the element (FIG. 5) or have a straight front face. There are many problems associated with these types of print elements. With the front face step, front face wiping is difficult. Even with a straight face, wiping may not be completely reliable. For example, if a dicing blade does not completely pass through the print element, a burr is left on the front face which can affect wiping blade contact. However, dicing completely through the wafer to eliminate the burr causes its own problems. When the saw blade passes completely through the print element, it comes into contact with print element mounting tape (dicing tape) below the print element wafer, which is usually of a plastic composition having an adhesive on a surface thereof. Cutting through a portion of the dicing tape loads up the dicing blade, causing excessive blade wear, and the blade picks up dicing tape material thereon. This contaminates the dicing blade and the front face of the die.
Chipping or contamination around the nozzle face is undesirable. It leads to ink jet nozzle directionality problems and wiping problems. Replacing the dicing blade frequently to minimize contamination is a costly alternative, especially when a resin blade is used which is expensive and already has a short useful life.
Another problem with both the straight front face and the forward step is that during manufacture, individual print elements are bonded to a heat sink substrate on a PC board. The substrate has a thin layer of a bonding adhesive such as screen-printed silver filled epoxy on top of a portion of the substrate serving as the heat sink. The epoxy is used to bond the individual print element to the substrate. Pressing of the print element onto the epoxy during assembly occasionally causes excess epoxy to extend around the edges of the print element. Any excess die bonding adhesive between the print element and the heat sink that flows onto the front face of the print element interferes with wiping operations and subsequent printing operations of the print element.
Additionally, top and bottom edges of the front face may be sharp or ragged. This can cause excessive wear on a wiping blade which traverses across the printhead, leading to unreliable wiping, inadequate contact, contamination of the front nozzle face and early replacement of the wiper blade.
U.S. Pat. No. 5,057,853, assigned to the same assignee as the present invention, discloses an alternative embodiment which forms a printhead die which has a recessed face. After bonding of heater and channel plate wafers, a first dicing cut is made from the channel side through the channel plate and partially through the heater plate to form a front nozzle face. Subsequently, a second cut is performed from the heater side to provide a recessed step. This has disadvantages. The bottom edge of the already formed front nozzle face may be affected by the back cut, most likely leaving a sharp or ragged edge on the bottom of the front nozzle face where the front face and the back cut adjoin. Further, diced fragments of the material cut during the back cut are expelled toward the front nozzle face from the dicing blade during the back cut and may cause contamination of the previously formed nozzle face surface. Any of these aforementioned disadvantages compromise the quality of the front nozzle face surface. These may cause ink jet directionality problems or may affect performance of a wiping blade which traverses laterally across the entire front face of the printhead, the blade requiring precise contact for best results. Any cracks, large nicks, or sharp edges in the front face surface can affect the reliability of wiper blade cleaning due to uneven or incomplete contact and may result in excessive wear to the wiper blade which can lead to directionality or other ink jet problems.
Alternately in this reference, rather than a straight cut from the heater side, an angled second cut can be made from the channel side to provide a recessed angled surface. However, to accomplish this, the blade itself is angled and the cutting operation is performed through the first cut, i.e., both cuts are from the channel side. Since the width of the first cut is narrow, even if a very thin blade is used there will be highly limited angular adjustment. This reference cannot provide an angled surface of more than about 10 degrees to the vertical. Additionally, due to the small tolerances and the close proximity of adjacent channel plate components, any misplacement of the angled blade may chip or damage the wafer components. Further, due to the necessity of a narrow blade, blade flex may cause a non-uniform or ragged edge surface.
There is a need for a thermal ink jet print element that better enables front face wiping and provides more reliable print head maintenance.
There also is a need for a method of printhead element manufacture which provides a better quality front face surface having less sharp edge surfaces.